gh-92203: Add closure support to exec(). (#92204)

Add a closure keyword-only parameter to exec(). It can only be specified when exec-ing a code object that uses free variables. When specified, it must be a tuple, with exactly the number of cell variables referenced by the code object. closure has a default value of None, and it must be None if the code object doesn't refer to any free variables.

Lib/test/test_builtin.py

@@ -24,7 +24,7 @@ from functools import partial
 from inspect import CO_COROUTINE
 from itertools import product
 from textwrap import dedent
-from types import AsyncGeneratorType, FunctionType
+from types import AsyncGeneratorType, FunctionType, CellType
 from operator import neg
 from test import support
 from test.support import (swap_attr, maybe_get_event_loop_policy)
@@ -772,6 +772,84 @@ class BuiltinTest(unittest.TestCase):
         finally:
             sys.stdout = savestdout
 
+    def test_exec_closure(self):
+        def function_without_closures():
+            return 3 * 5
+
+        result = 0
+        def make_closure_functions():
+            a = 2
+            b = 3
+            c = 5
+            def three_freevars():
+                nonlocal result
+                nonlocal a
+                nonlocal b
+                result = a*b
+            def four_freevars():
+                nonlocal result
+                nonlocal a
+                nonlocal b
+                nonlocal c
+                result = a*b*c
+            return three_freevars, four_freevars
+        three_freevars, four_freevars = make_closure_functions()
+
+        # "smoke" test
+        result = 0
+        exec(three_freevars.__code__,
+            three_freevars.__globals__,
+            closure=three_freevars.__closure__)
+        self.assertEqual(result, 6)
+
+        # should also work with a manually created closure
+        result = 0
+        my_closure = (CellType(35), CellType(72), three_freevars.__closure__[2])
+        exec(three_freevars.__code__,
+            three_freevars.__globals__,
+            closure=my_closure)
+        self.assertEqual(result, 2520)
+
+        # should fail: closure isn't allowed
+        # for functions without free vars
+        self.assertRaises(TypeError,
+            exec,
+            function_without_closures.__code__,
+            function_without_closures.__globals__,
+            closure=my_closure)
+
+        # should fail: closure required but wasn't specified
+        self.assertRaises(TypeError,
+            exec,
+            three_freevars.__code__,
+            three_freevars.__globals__,
+            closure=None)
+
+        # should fail: closure of wrong length
+        self.assertRaises(TypeError,
+            exec,
+            three_freevars.__code__,
+            three_freevars.__globals__,
+            closure=four_freevars.__closure__)
+
+        # should fail: closure using a list instead of a tuple
+        my_closure = list(my_closure)
+        self.assertRaises(TypeError,
+            exec,
+            three_freevars.__code__,
+            three_freevars.__globals__,
+            closure=my_closure)
+
+        # should fail: closure tuple with one non-cell-var
+        my_closure[0] = int
+        my_closure = tuple(my_closure)
+        self.assertRaises(TypeError,
+            exec,
+            three_freevars.__code__,
+            three_freevars.__globals__,
+            closure=my_closure)
+
+
     def test_filter(self):
         self.assertEqual(list(filter(lambda c: 'a' <= c <= 'z', 'Hello World')), list('elloorld'))
         self.assertEqual(list(filter(None, [1, 'hello', [], [3], '', None, 9, 0])), [1, 'hello', [3], 9])